Ecki,
I'll try to find any image of Micrasterias truncata taken with simple polarisation. If I shall not be able to find Micrasterias I send another Desmid, for example Netrium.
I'm looking for the the extemely rare V-IM magnification changer for the E800 scope. If you have seen a listing or have one for sale please let me know.
Here is the sample of simple polarization of Netrium, as I promised. Unfortunately I haven't managed to find any Micrasterias without the retarders now. If I have opportunity to catch Micrasterias truncata I'll take photo without the retarders.